Composition and process for electrodepositing a black chromium deposit

ABSTRACT

A black chromium electroplating solution comprising a source of hexavalent chromium ions, and an effective blackening amount of selenium.

c I Umted States Patent 1 1 1111 3,909,404

Boycott Sept. 30, 1975 [54] COMPOSITION AND PROCESS FOR 2985,567 5/1961 Pinkerton 204/51 X ELECTRODEPOSYIING A BLACK Ifilhjzssin :2 son 1 CHROMIUM DEPOSIT 3,514,380 5/1970 Tuchewicz et 204/51 [75] Inventor; William A, Boycott, Old Castle, 3.661.733 5/1972 Roggendorf 1 v v 204/51 Canada 3.723.261 3/1973 Byers et ul. 204 51 [73] Assignec: Oxy Metal Industries Corporation, 1

Warren, Mich- Primary Examiner-G. L. Kaplan [221 Filed: Feb. 26 1973 Attorney, Agent, or Firm-B. F. Claeboe [21] Appl. No.: 335,602

7 57 ABSTRACT [52] US. Cl 204/43 R; 204/51 [51] a CZSD 3/087; CZSD 3/56 A black chromium electroplating solution comprising Fleld of Search R a Source of hexavalent chromium ions, and an effec [56] R f Ct d tive blackening amount of selenium.

e erences 1 e UNlTED STATES PATENTS 7 C'aims, N0 Drawings 21126.538 3/1958 Hunter et 211... 204/51 X C'GMPOSITION AND PROCESS FOR ELECTRODEPOSITING A BLACK CHROMIUM DEPOSIT BACKGROUND OF THE INVENTION 1 Black chromiumis a term used to describe .the electrodeposition of chromium'which' is black -in appearance,-and which is formed during the electrodeposition of a hexavalent chromium containing solution which is substantially lacking in thepresence of sulfate Various references have described methods of-producing black chromium, such as US. Pat. Nos. 3,419,481 and 3,511,759.

Prior art methods have resulted in a grey, black deposit of chromium which is generally undesirable from a decorative point of view. It has been found by this invention that a simplified means of obtaining black chromium has been obtained.

SUMMARY or THE. INVENTION i A black chromium deposit can be obtained from a chromium electroplating bath having fluoride ions and an effective blackening amount of selenium ions. It has been surprisingly found that selenium is particularly effective in giving a black chromium depoit, when the amount of selenium is' present'in an amount of at .least 0.1 grams/liter. The fact that the use of selenium will give a black deposit is particularly surprising, since tellurium, in equivalent amounts, will normally not give a black chromium deposit.

DESCRIPTION OF PREFERRED EMBODIMENTS Applicants invention is directed to a chromium electroplating solution which will result in a black chromium deposit. The electroplating solution can be described as having a source of chromium ions, preferably, hexavalent chromium ions. Chromium may be introduced into the bath as any available grade of chromic acid (Cl O3), as well as any other source of chromium ions.

Selenium that is used in the present application should contain an effective blackening amount, preferably, at least 0.1 grams/liter of selenium ions. There is no upper limit that may be employed, other than a practical limit in that the more selenium that is employed, the more costly will be the deposition of black chromium. A practical upper limit will be approximately 10 grams/liter.

The selenium may be introduced into the bath in any form that will dissolve in the bath and give the desired amount of selenium ions, such as selenium metal, selenium oxide, and the like.

In addition, it has been found that a source of fluoride ions should be employed in order to give good coverage to the black chromium deposit, preferably, the amount of fluoride ions that may be employed in order to give good coverage to the black chromium deposit, preferably, the amount of fluoride ions that may be employed ranges from about 0.5 grams/liter to about 2 grams/liter.

Fluoride ions may be introduced into the bath in any form which will dissolve'in the bath and give the desired amount of fluoride ions, such as, hydrofluoric acid, fluoboric acid, fluosilicic acid and bath soluble alkali metal, alkaline'earth metal, heavy metal and ammonium salts thereof.

In order to obtain the black chromium deposit sulfate ions should normally not be-present. If sulfate ions are present, then a bright chromium deposit willbe obtained,: rather than the desired black chromium deposit. In order to be sure that sulfate ions would not be present in the bath, a metal ion may be employed to decrease. the content .by precipitating the sulfate ions. Preferredmetal ions that may be employed, 'are alkali oralkali'ne' earth metal-ions, most preferably, barium, calcium; and the like. The lower limit of the metal that may beemployed is about 5- grams/liter calculated as barium hydroxide. The upper limitwould be a practical upper limit, due to costs, preferably about 100 grams/- liter (calculated'asbarium hydroxide); most preferably, the amount of metal that may be employed'is about I to 50 grams/liter'(calcul'ated as barium hydroxide).

Most preferably, the metal that will be employed is bar ium material, such'as barium hydroxide.

Other materials may also be present in the black chromium electrodepositing bath such as surfactants, spray suppressants, and" the like, as are normally used in the art of chromium-electroplating.

Uniform black chromium containing deposits are readily obtained over a current density range of about 30 asfto about 1500 asf amps/sh ft). The temperature 'of'th'e aqueous acidic chromium electroplating solution can be 'widely'employedsuch' as'from 10C to 45C.

Having described in general applicants invention, listed below are examples that may be employed to further describe preferred embodiments.

All temperatures are in degrees Centigrade andall weights are percentages by weight unless otherwise indicated. I

EXAMPLE I A steel panel with a bright nickel electrodeposit was inserted into 21 Hull cell for electroplating a chromium employing the following electroplating solutions.

A chromium electroplating solution containing 100-400 grams/liter of chromium trioxide was prepared having the following amount of additional materials: Cr O 7 Grams/liter; sodium hydroxide 57.5 grams/liter; K Si F 1.0 2.0 grams/liter; and selenium ions 100200 grams/liter. The chromium electroplating solution was used in the Hull cell and chromium was electrodeposited at a temperature of 60F. An uniform, black chromium deposit was obtained over 50 to milliliters of the Hull cell panel.

EXAMPLE II In order to improve the stability of the electroplating solution, the following formulation was prepared. A Hull cell panel was prepared by electrodepositing bright nickel on to steel. The following formulation was substantially more improved, than the formulation of Example I. The electroplating solution contained: 400 grams/liter of CrO 2O grams/liter of barium hydroxide, 2.0 grams/liter of K Si F and 2 grams/liter of SeO. A uniform chromium deposit was obtained in the cell panel.

EXAMPLE Ill ide; l gram/liter of barium carbonate; and 2 grams/liter K Si F The solution was electrodeposited in a Hull cell having a steel panel which had a bright nickel electrodeposit thereon. The solution had a narrow, black high current density band which was grey to 80 milliliters. The deposit was highly undesireable for a black chromium deposit.

To the above solution was added, 100 milligrams/- liter of tellurium and a similar panel was electrodeposited in a Hull cell using equivalent deposition rates. No change was found in the deposit. Additional tellurium was added to the above solution until a concentration of 400 milligrams/liter was obtained. The deposit was likewise unsatisfactory.

It has also been found that if the direct current is periodically interrupted during the electrodeposition of black chromium, a more uniform black deposit can be obtained over a wider current density range employing this technique. This can be best described as follows; in a 30 second period, the current is on (electrodeposition occurs) for more time than it is off. Preferably, the current is on 75% of the time and off 25% of the time in a 30 second period. The most preferred cycle is that of 7 seconds on and 2 seconds off.

EXAMPLE IV When utilizing the procedure of Example I in a Hull cell panel, and containing: 1.0 grams/liter of selenium dioxide, with a temperature of 110F., minutes of depositing chromium in a Hull cell at 5 amps, a uniform black deposit was obtained over 50 millimeters of the panel. Employing a current interruption of 7 seconds on and 2 seconds off, during 5 minutes, to a similar panel, an excellent uniform black deposit was obtained over milliliters of the panel. Clearly, the use of current interruption gave a broader deposition of black chromium.

What is claimed is:

1. An aqueous acidic black chromium electroplating solution having fluoride ions in an amount of about 0.5 to about 2 g/l, comprising a about 100-400 g/] CrO in the absence of sulfate ions, and an effective blackening amount of selenium in the amount of at least about 0.1 g/l.

2. A solution as defined in claim 1, wherein the selenium ions are present in an amount of from 0.1 to 10 g/l and an alkaline earth metal ion is present in an amount calculated as barium hydroxide of from about 5.0 to 100 g/l.

3. A process of electrodepositing black chromium from an acidic chromium bath, comprising passing a current from an anode to a cathode through the solution of claim 1 to form a uniform black chromium deposit.

4. A process as defined in claim 3, wherein the current is interrupted during a 30 second period having a cycle such that the current is on more than off.

5. A process as defined in claim 4, wherein the current is on for of the time and is off 25% of the time over a 30 second period.

6. A process as defined in claim 4, wherein the cycle is 7 seconds on and 2 seconds off.

7. A process as defined in claim 3, wherein selenium ions are present in an amount of from about 0.1 to 10 g/l and an alkaline earch metal ion is present in an amount calculated as barium hydroxide of from about 5.0 to g/l. 

1. AN AQUEOUS ACIDIC BLACK CHROMIUM ELECTROPLATING SOLUTION HAVING FLUORIDE IONS IN AN AMOUNT OF ABOUT 0.5 TO ABOUT 2G/L, COMPRISING A ABOUT 100-400G/L CRO3 IN THE ABSENCE OF SULFATE IONS, AND AN EFFECTIVE BLACKENING AMOUNT OF SELENIUM IN THE AMOUNT OF AT LEAST ABOUT 0.1 G/L.
 2. A solution as defined in claim 1, wherein the selenium ions are present in an amount of from 0.1 to 10 g/l and an alkaline earth metal ion is present in an amount calculated as barium hydroxide of from about 5.0 to 100 g/l.
 3. A process of electrodepositing black chromium from an acidic chromium bath, comprising passing a current from an anode to a cathode through the solution of claim 1 to form a uniform black chromium deposit.
 4. A process as defined in claim 3, wherein the current is interrupted during a 30 second period having a cycle such that the current is on more than off.
 5. A process as defined in claim 4, wherein the current is on for 75% of the time and is off 25% of the time over a 30 second period.
 6. A process as defined in claim 4, wherein the cycle is 7 seconds on and 2 seconds off.
 7. A process as defined in claim 3, wherein selenium ions are present in an amount of from about 0.1 to 10 g/l and an alkaline earch metal ion is present in an amount calculated as barium hydroxide of from about 5.0 to 100 g/l. 